There's nothing wrong with her old house other than it's a bit too large for two people, and she's not as young as she once was. My sister and I have encouraged her to stay put at least until this tax issue is resolved.
You bring up an excellent example. My mother wants to “trade down” now herself. She can’t. She considered moving here to Kentucky for that reason.
When we wanted out of the neighborhood in Florida our friends asked why we didn’t just move farther out from the city. I said we are not paying $75k more for the same size house and 3 times the property taxs to boot. Time to get out of the state.
At least we don’t live in one of the European socialist paradises where we have to get permission and on a waiting list in order to relocate.